SDL按钮文本经约1399次渲染迭代后消失问题排查

问题现象 #

开发的SDL按钮文本会在约1399次渲染迭代后消失，全程调用同一个类函数，排除函数本身逻辑问题。对比消失前后的状态发现：类成员SDL_Surface* buttonTextSurface在文本消失时指向NULL。

消失前状态 #

• 按钮文本正常显示，buttonTextSurface指向有效内存地址
• 相关成员变量状态无异常

消失后状态 #

• buttonTextSurface变为NULL
• 按钮文本无法渲染显示

相关代码 #

#include"include/SDL.h"
#include<iostream>
#include<Windows.h>
#include"include/SDL_ttf.h"
#include<conio.h>
SDL_Window* window = SDL_CreateWindow("Button Example", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, SDL_WINDOW_SHOWN);
SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
TTF_Font* font;
using namespace std;
class Button {
    SDL_Rect Letter_Button;
    char text_for_button;
    bool Button_pushed;
    bool Button_hovered;
    COORD Position;
    int Shadow_offset;
    int Button_Size;
    SDL_Rect buttonShadow;
    SDL_Surface* buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 }); //text Color
    SDL_Texture* buttonTextTexture = SDL_CreateTextureFromSurface(renderer, buttonTextSurface);
public:
    Button() :
        Button_pushed(0), Button_hovered(0), Position({ 0,0 }), Shadow_offset(5), Button_Size(0) {}
    Button(short x_axis, short y_axis) :
        Button_pushed(0), Button_hovered(0), Position({ x_axis, y_axis }) {}
    void Set_Button(char Alphabet, COORD Position, int Button_Size) {
        cout << "enterd\n";
        text_for_button = Alphabet;
        this->Position = Position;
        this->Button_Size = Button_Size;
        Letter_Button = { Position.X, Position.Y, Button_Size, Button_Size };
        buttonShadow = { Position.X + Shadow_offset, Position.Y + Shadow_offset, Button_Size, Button_Size };
        buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 }); //text Color
    }
    void Diplay_Shadow() {
        SDL_SetRenderDrawColor(renderer, 75, 75, 75, 50);
        SDL_RenderFillRect(renderer, &buttonShadow);
    }
    void Display_Button() {
        Diplay_Shadow();
        buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 }); //text Color
        buttonTextTexture = SDL_CreateTextureFromSurface(renderer, buttonTextSurface);
        SDL_SetRenderDrawColor(renderer, 255, 65, 65, 50);
        SDL_RenderFillRect(renderer, &Letter_Button);
        SDL_RenderCopy(renderer, buttonTextTexture, NULL, &Letter_Button);
        //if(Button_pushed) //change color
        //if(Button_hover) //change color
    }
};
Button Normal_Letters[26];

int main(int argc, char* argv[]) {
    SDL_Init(SDL_INIT_VIDEO);
    TTF_Init();
    font = TTF_OpenFont("arial.ttf", 1000);//16  //max : 7332
    // Load a font to use for the button text
    // Create a surface for the button text
    SDL_Surface* buttonTextSurface = TTF_RenderText_Solid(font, "A", { 0, 0, 255 }); //text Color
    int x;
    // Create a texture from the surface
    SDL_Texture* buttonTextTexture = SDL_CreateTextureFromSurface(renderer, buttonTextSurface);
    // Create a rectangle for the button position and dimensions
    SDL_Rect buttonRect{ 10, 10, 100, 100 };
    int Shadow_offset = 5;
    SDL_Rect button_Shadow{ 10 + Shadow_offset, 10 + Shadow_offset, 100, 100 };
    bool buttonHovered = false, Button_Pushed = 0;
    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
    //cout << test << "\n";
    while (true) {
        SDL_Event event;
        if (_kbhit()) {
            x = _getch() - '0';
            cout << "df\n";
        }
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT || event.key.keysym.sym == SDLK_ESCAPE) {
                // Close the window and quit the game
                SDL_DestroyTexture(buttonTextTexture);
                SDL_FreeSurface(buttonTextSurface);
                TTF_CloseFont(font);
                SDL_DestroyRenderer(renderer);
                SDL_DestroyWindow(window);
                SDL_Quit();
                exit(0);
                return 0;
            }
            if (event.type == SDL_MOUSEMOTION) {
                // Check if the mouse is hovering over the button rectangle
                int x, y;
                SDL_GetMouseState(&x, &y);
                buttonHovered = (x >= buttonRect.x && x < buttonRect.x + buttonRect.w && y >= buttonRect.y && y < buttonRect.y + buttonRect.h);
            }
            if (event.type == SDL_MOUSEBUTTONUP) {
                // Check if the mouse click was within the button rectangle
                int x, y;
                SDL_GetMouseState(&x, &y);
                if (x >= buttonRect.x && x < buttonRect.x + buttonRect.w && y >= buttonRect.y && y < buttonRect.y + buttonRect.h) {
                    // The mouse click was within the button, so do something
                    std::cout << "Button clicked!\n";
                    Button_Pushed = !Button_Pushed;
                    Shadow_offset = Shadow_offset * -1;
                    if (Button_Pushed) {
                        buttonRect = { 15, 15, 95, 95 };
                        button_Shadow.x = 10;
                        button_Shadow.y = 10;
                    }
                    else
                    {
                        buttonRect = { 10, 10, 100, 100 };
                        button_Shadow.x = 10 + Shadow_offset;
                        button_Shadow.y = 10 + Shadow_offset;
                    }
                }
            }
        }
        // Render the button
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderClear(renderer);
        //for (size_t i = 0; i < 26; i++)
        //  Normal_Letters[i].text_for_button = char(i + 65);
        Normal_Letters[1].Set_Button('B', { 200, 200 }, 100);
        Normal_Letters[1].Display_Button();
        if (_kbhit())
            x = _getch() - '0';
        if (Button_Pushed || 1)//if not Pressed then show shadow
        {
            SDL_SetRenderDrawColor(renderer, 75, 75, 75, 200);
            SDL_RenderFillRect(renderer, &button_Shadow);
        }
        if (buttonHovered) {
            // Use cyan and yellow for the button color when it is hovered
            SDL_SetRenderDrawColor(renderer, 0, 255, 255, 255);
            SDL_RenderFillRect(renderer, &buttonRect);
            //SDL_SetRenderDrawColor(renderer, 255, 255, 0, 255);
            //SDL_RenderDrawRect(renderer, &buttonRect);
        }
        else {
            // Use white for the button color when it is not hovered
            SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        }
        SDL_RenderFillRect(renderer, &buttonRect);
        SDL_RenderCopy(renderer, buttonTextTexture, NULL, &buttonRect);
        SDL_RenderPresent(renderer);
    }
}

问题根源 #

1. 内存泄漏耗尽资源：Display_Button()和Set_Button()中每次调用都会创建新的buttonTextSurface和buttonTextTexture，但从未释放旧资源。SDL的Surface、Texture等系统资源有限，反复创建不释放会导致内存耗尽，最终TTF_RenderText_Solid()和SDL_CreateTextureFromSurface()无法分配内存，返回NULL。
2. 初始化顺序错误：全局Button数组Normal_Letters[26]在main()前初始化，此时font还未被TTF_OpenFont()初始化，构造函数中创建buttonTextSurface的操作会使用未初始化的font，引发未定义行为。
3. 主循环重复初始化按钮：主循环每次迭代都调用Normal_Letters[1].Set_Button()，属于无意义操作，还会加剧内存泄漏。

修复方案 #

1. 及时释放旧资源 #

在重新创建Surface和Texture前，释放旧的资源：

void Display_Button() {
    Diplay_Shadow();
    // 释放旧资源
    if (buttonTextSurface != nullptr) {
        SDL_FreeSurface(buttonTextSurface);
        buttonTextSurface = nullptr;
    }
    if (buttonTextTexture != nullptr) {
        SDL_DestroyTexture(buttonTextTexture);
        buttonTextTexture = nullptr;
    }
    buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 });
    buttonTextTexture = SDL_CreateTextureFromSurface(renderer, buttonTextSurface);
    SDL_SetRenderDrawColor(renderer, 255, 65, 65, 50);
    SDL_RenderFillRect(renderer, &Letter_Button);
    SDL_RenderCopy(renderer, buttonTextTexture, NULL, &Letter_Button);
}

Set_Button()中同样需要释放旧Surface：

void Set_Button(char Alphabet, COORD Position, int Button_Size) {
    cout << "enterd\n";
    text_for_button = Alphabet;
    this->Position = Position;
    this->Button_Size = Button_Size;
    Letter_Button = { Position.X, Position.Y, Button_Size, Button_Size };
    buttonShadow = { Position.X + Shadow_offset, Position.Y + Shadow_offset, Button_Size, Button_Size };
    // 释放旧Surface
    if (buttonTextSurface != nullptr) {
        SDL_FreeSurface(buttonTextSurface);
        buttonTextSurface = nullptr;
    }
    buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 });
}

2. 修正初始化顺序 #

将类成员Surface和Texture初始化为NULL，避免构造函数中使用未初始化的font：

class Button {
    // ... 其他成员变量 ...
    SDL_Surface* buttonTextSurface = nullptr;
    SDL_Texture* buttonTextTexture = nullptr;
public:
    Button() :
        Button_pushed(0), Button_hovered(0), Position({ 0,0 }), Shadow_offset(5), Button_Size(0),
        buttonTextSurface(nullptr), buttonTextTexture(nullptr) {}
    // ... 其他构造函数 ...
};

3. 移除主循环中的重复初始化 #

将按钮初始化移到主循环外，只执行一次：

int main(int argc, char* argv[]) {
    // ... SDL、TTF、font初始化 ...
    Normal_Letters[1].Set_Button('B', { 200, 200 }, 100);
    while (true) {
        // ... 事件处理 ...
        SDL_RenderClear(renderer);
        Normal_Letters[1].Display_Button();
        // ... 其他渲染操作 ...
    }
}

4. 添加错误检查 #

调用SDL/TTF函数时检查返回值，便于调试：

buttonTextSurface = TTF_RenderText_Solid(font, &text_for_button, { 0, 0, 255 });
if (buttonTextSurface == nullptr) {
    cout << "TTF渲染失败: " << TTF_GetError() << endl;
}
buttonTextTexture = SDL_CreateTextureFromSurface(renderer, buttonTextSurface);
if (buttonTextTexture == nullptr) {
    cout << "创建纹理失败: " << SDL_GetError() << endl;
}

内容的提问来源于stack exchange，提问作者Wakeel Furqan Ahmed